Effect of CXCL12 and Its Receptors on Unpredictable Renal Cell Carcinoma

Chemokines are chemotactic cytokines that participate in numerous cell functions during hematopoiesis, morphogenesis, inflammation, neovascularization, and autoimmune diseases and cancer. They achieve their functions on binding to their G protein-coupled receptors. CXCL12, or stromal cell-derived factor-1, is a homeostatic chemokine secreted by fibroblasts, macrophages, and endothelial cells. It binds to CXC receptor 4 (CXCR4), also known as fusin (CD184), and alternate CXC receptor 7 (CXCR7), also known as atypical chemokine receptor 3. The CXCL12/CXCR4 axis participates in homing of hematopoietic stem cells and the development and production of B and T lymphocytes, plasmacytoid dendritic cells, and natural killer cells. It has been examined in > 20 different malignancies. CXCL12 plays an important role in tumor metastasis because it mediates the migration of tumor cells through the endothelial vessel wall and extracellular matrix. Its expression has been highest in common metastatic sites such as the brain, bone marrow, lymph nodes, and liver. CXCR4 is expressed by tumor cells in prostate, breast, lung, and other malignancies. Numerous studies have shown its correlation with a poor prognosis, recurrence-free survival, and poor overall survival. The present review has addressed the structure and function of CXCL12 and its receptors and the effect CXCL12/CXCR4 axis has on the pathogenesis and clinical development of renal cell carcinoma, one of the most aggressive cancers in urology, with limited therapeutic options.     

Biological/pathological functions of the CXCL12/CXCR4/CXCR7 axes in the pathogenesis of bladder cancer

CXC chemokine ligand 12 (CXCL12) is an important member of the CXC subfamily of chemokines, and has been extensively studied in various human body organs and systems, both in physiological and clinical states. Ligation of CXCL12 to CXCR4 and CXCR7 as its receptors on peripheral immune cells gives rise to pleiotropic activities. CXCL12 itself is a highly effective chemoattractant which conservatively attracts lymphocytes and monocytes, whereas there exists no evidence to show attraction for neutrophils. CXCL12 regulates inflammation, neo-vascularization, metastasis, and tumor growth, phenomena which are all pivotally involved in cancer development and further metastasis. Generation and secretion of CXCL12 by stromal cells facilitate attraction of cancer cells, acting through its cognate receptor, CXCR4, which is expressed by both hematopoietic and non-hematopoietic tumor cells. CXCR4 stimulates tumor progression by different mechanisms and is required for metastatic spread to organs where CXCL12 is expressed, thereby allowing tumor cells to access cellular niches, such as the marrow, which favor tumor cell survival and proliferation. It has also been demonstrated that CXCL12 binds to another seven-transmembrane G-protein receptor or G-protein-coupled receptor, namely CXCR7. These studies indicated critical roles for CXCR4 and CXCR7 mediation of tumor metastasis in several types of cancers, suggesting their contributions as biomarkers of tumor behavior as well as potential therapeutic targets. Furthermore, CXCL12 itself has the capability to stimulate survival and growth of neoplastic cells in a paracrine fashion. CXCL12 is a supportive chemokine for tumor neovascularization via attracting endothelial cells to the tumor microenvironment. It has been suggested that elevated protein and mRNA levels of CXCL12/CXCR4/CXCR7 are associated with human bladder cancer (BC). Taken together, mounting evidence suggests a role for CXCR4, CXCR7, and their ligand CXCL12 during the genesis of BC and its further development. However, a better understanding is still required before exploring CXCL12/CXCR4/CXCR7 targeting in the clinic.     

Chemokine expression in tumor-to-tumor metastasis

Chemokines play an important role in cancer metastasis by modulating the directional cell movement and migration of tumor cells. The most commonly overexpressed chemokine receptor in human cancer is CXCR4. Once activated by its ligand CXCL12 (stromal cell-derived factor-1 ligand/SDF1), CXCR4 stimulates several key migratory, proliferative and survival signaling cellular pathways. CXCR4 is expressed in small-cell lung carcinoma (SCLC) cells and other tumors. To further characterize the role of chemokines in tumor-to-tumor metastasis, we analyzed the tissue expression of CXCR4 and CXCL12 in the surgical specimen of a patient with this phenomenon. We performed immunohistochemical analysis for the expression of CXCR4 and CXCL12 in metastatic tumor tissue of a 69-year-old Caucasian male with extensive SCLC metastatic to a renal oncocytoma. The oncocytoma tissue harboring SCLC showed CXCL12 expression, but not CXCR4. A high expression of the two molecules was found in a normal renal parenchymal control. Our results suggest that CXCR4 and CXCL12 plays a role in this condition, but their expression may be affected by the microenvironment of the harboring malignancy. Further characterization of these phenomena is needed to shed light on the biological mechanisms of tumor metastasis.     

Potential of CXCR4 antagonists for the treatment of metastatic lung cancer

Despite advances in surgery, chemotherapy and radiotherapy over the last decades, the death rate from lung cancer has remained largely unchanged, which is mainly due to metastatic disease. Because of the overall poor prognosis, new treatment strategies for lung cancer patients are urgently needed, and targeting CXCR4 constitutes such a novel, attractive strategy. Tumor cell migration and metastasis share many similarities with leukocyte trafficking, which is critically regulated by chemokine receptors and adhesion molecules. Lung cancer cells express CXCR4 (CD184), a seven-transmembrane G-protein-coupled chemokine receptor. Stromal cells within the tumor microenvironment constitutively secrete stromal cell-derived factor-1 (SDF-1/CXCL12), the ligand for CXCR4. Activation of CXCR4 induces lung cancer cell migration and adhesion to stromal cells, which in turn provides growth- and drug-resistance signals to the tumor cells. CXCR4 antagonists, such as Plerixafor (AMD3100) and T140 analogues (TN14003/BKT140), can disrupt CXCR4-mediated tumor cell adhesion to stromal cells and sensitize lung cancer cells to cytotoxic drugs. Therefore, targeting the CXCR4–CXCL12 axis is a novel, attractive therapeutic approach in small-cell lung cancer and non-small-cell lung cancer. In this article, we summarize data about the cellular and molecular microenvironment in small-cell lung cancer and non-small-cell lung cancer, as well as the role of CXCR4 in tumor–stroma crosstalk. In addition, we review the current status of the preclinical and clinical development of CXCR4 antagonists.     

CXCL12／CXCR4生物学轴诱导前列腺癌骨转移的作用机制研究进展

研究发现趋化因子CXCL12（Stromal—derived factor-1,SDF-1）和受体CXCR4[chemokine（C—X—Cmotif）receptor4]广泛表达于组织和器官上,相关的研究发现其与前列腺癌细胞的黏附、侵袭、增殖和生存有关,并认为其在前列腺癌骨转移的发生中发挥重要作用。通过阐明CXCL12／CXCR4生物学轴和前列腺癌骨转移之间的关系,从而寻找有助于疾病治疗的新途径。     

Potential of CXCR4 antagonists for the treatment of metastatic lung cancer

Despite advances in surgery, chemotherapy and radiotherapy over the last decades, the death rate from lung cancer has remained largely unchanged, which is mainly due to metastatic disease. Because of the overall poor prognosis, new treatment strategies for lung cancer patients are urgently needed, and targeting CXCR4 constitutes such a novel, attractive strategy. Tumor cell migration and metastasis share many similarities with leukocyte trafficking, which is critically regulated by chemokine receptors and adhesion molecules. Lung cancer cells express CXCR4 (CD184), a seven-transmembrane G-protein-coupled chemokine receptor. Stromal cells within the tumor microenvironment constitutively secrete stromal cell-derived factor-1 (SDF-1/CXCL12), the ligand for CXCR4. Activation of CXCR4 induces lung cancer cell migration and adhesion to stromal cells, which in turn provides growth- and drug-resistance signals to the tumor cells. CXCR4 antagonists, such as Plerixafor (AMD3100) and T140 analogues (TN14003/BKT140), can disrupt CXCR4-mediated tumor cell adhesion to stromal cells and sensitize lung cancer cells to cytotoxic drugs. Therefore, targeting the CXCR4-CXCL12 axis is a novel, attractive therapeutic approach in small-cell lung cancer and non-small-cell lung cancer. In this article, we summarize data about the cellular and molecular microenvironment in small-cell lung cancer and non-small-cell lung cancer, as well as the role of CXCR4 in tumor-stroma crosstalk. In addition, we review the current status of the preclinical and clinical development of CXCR4 antagonists.     

Chemokine CXCL12 in cancer

CXCL12, also known as stromal cell-derived factor 1, is a member of the CXC family, which locates on the 10th chromosome and produces by the stromal cells. It is known that CXCR4 and CXCR7 are the two receptors of chemokine CXCL12. Many studies show that the chemokine CXCL12 plays an important role in cancer progression, including proliferation, metastasis and angiogenesis. Therefore, the chemokine CXCL12 is expected to become a novel target for the gene therapy of cancer.     

Stromal Derived Factor-1 (SDF-1/CXCL12) and CXCR4 in renal cell carcinoma metastasis

Renal cell carcinoma (RCC) is characterized by organ-specific metastases. The chemokine stromal derived factor-1 (SDF-1/CXCL12) and its receptor CXCR4 have been suggested to regulate organ-specific metastasis in various other cancers. On this basis, we hypothesized that the biological axis of CXCL12 via interaction with its receptor, CXCR4, is a major mechanism for RCC metastasis. We demonstrated that CXCR4 was significantly expressed on circulating cytokeratin+ RCC cells from patients with known metastatic RCC. We detected up-regulation of CXCR4 mRNA and protein levels on a human RCC cell line by either knockdown of the von Hippel-Lindau (VHL) tumor suppressor protein, or incubating the cells under hypoxic conditions. The enhanced CXCR4 expression was mediated through the interaction of the Hypoxia Inducible Factor-1α (HIF-1α) with the promoter region of the CXCR4 gene. Furthermore, the expression of CXCR4 on human RCC directly correlated with their metastatic ability in vivo in both heterotopic and orthotopic SCID mouse models of human RCC. Neutralization of CXCL12 in SCID mice abrogated metastasis of RCC to target organs expressing high levels of CXCL12; without altering tumor cell proliferation, apoptosis, or tumor-associated angiogenesis. Therefore, our data suggest that the CXCL12/CXCR4 biological axis plays an important role in regulating the organ-specific metastasis of RCC.     

CXCL12/CXCR4生物学轴诱导前列腺癌骨转移的作用机制研究进展

研究发现趋化因子CXCL12(Stromal-derived factor-1,SDF-1)和受体CXCR4[chemokine (C-X-C motif) receptor 4]广泛表达于组织和器官上,相关的研究发现其与前列腺癌细胞的黏附、侵袭、增殖和生存有关,并认为其在前列腺癌骨转移的发生中发挥重要作用.通过阐明CXCL12/CXCR4生物学轴和前列腺癌骨转移之间的关系,从而寻找有助于疾病治疗的新途径.     

Role of chemokines in tumor growth

Chemokines play a paramount role in the tumor progression. Chronic inflammation promotes tumor formation. Both tumor cells and stromal cells elaborate chemokines and cytokines. These act either by autocrine or paracrine mechanisms to sustain tumor cell growth, induce angiogenesis and facilitate evasion of immune surveillance through immunoediting. The chemokine receptor CXCR2 and its ligands promote tumor angiogenesis and leukocyte infiltration into the tumor microenvironment. In harsh acidic and hypoxic microenvironmental conditions tumor cells up-regulate their expression of CXCR4, which equips them to migrate up a gradient of CXCL12 elaborated by carcinoma-associated fibroblasts (CAFs) to a normoxic microenvironment. The CXCL12-CXCR4 axis facilitates metastasis to distant organs and the CCL21-CCR7 chemokine ligand-receptor pair favors metastasis to lymph nodes. These two chemokine ligand-receptor systems are common key mediators of tumor cell metastasis for several malignancies and as such provide key targets for chemotherapy. In this paper, the role of specific chemokines/chemokine receptor interactions in tumor progression, growth and metastasis and the role of chemokine/chemokine receptor interactions in the stromal compartment as related to angiogenesis, metastasis, and immune response to the tumor are reviewed.     

CXCL12/SDF1 expression by breast cancers is an independent prognostic marker of disease-free and overall survival

The cytokine C-X-C motif chemokine 12 (CXCL12) is synthesised by metastasis target tissues and has been shown to attract tumour cells that express the receptor, C-X-C chemokine receptor type 4 (CXCR4). However, epigenetic silencing of CXCL12 has recently been reported to increase the metastatic potential of breast cancer cells and the reintroduction of the cytokine gene into MDA-MB-231 breast carcinoma cells decreases the number of metastases formed in vivo. We therefore wished to know whether CXCL12 expression correlates with relapse-free and overall survival in human breast cancer patients.The expression of C-X-C motif chemokine 12 (CXCL12) and C-X-C chemokine receptor type 4 (CXCR4) was analysed in 100 archival breast cancer samples by immunohistochemistry and in two breast cancer microarray datasets of 408 cases. Data were analysed by univariate and multivariate COX regression analyses.CXCL12 and CXCR4 are expressed by epithelial tumour cells and by stromal and endothelial cells. Microarray gene expression analysis and immunohistochemistry revealed that expression of CXCL12 but not of CXCR4 significantly correlates with disease-free and overall survival in oestrogen receptor-positive and -negative cancers. The expression of the oestrogen receptor α and that of CXCL12 do not correlate.CXCL12 is a strong, independent prognostic marker. We propose that saturation of the receptor through autocrine CXCL12 production reduces chemotaxis towards CXCL12-releasing metastasis target tissues.     

趋化因子CXCL12及其受体与肿瘤转移的关系

趋化因子CXCL12(C-X-C chemokine ligand 12)及其受体CXCR4(c-x-c chemokine receptor4)在胚胎发育、干细胞的迁移和各种免疫反应中发挥重要作用,是许多生理和病理过程中指导细胞运动的中心因素.最近发现肿瘤细胞的转移机制和白细胞的迁移相类似,趋化因子CXCL12及其受体与肿瘤的生长、侵袭、转移和分泌密切相关,动物实验表明CXCR4可能成为抑制肿瘤生长、转移的重要靶目标.本文将对趋化因子CXCL12及其受体CXCR4在肿瘤转移、进展中的作用以及与此相关的信号转导、调节因子进行综述.     

CXCR4 Regulates the Early Extravasation of Metastatic Tumor Cells In Vivo

Recent studies have demonstrated that the chemokine receptor CXCR4 plays a crucial role in organ-specific metastasis formation. Although a variety of studies showed the expression of chemokine receptors, in particular, CXCR4, by gastrointestinal tumors, the precise mechanisms of chemokine receptor-mediated homing of cancer cells to specific sites of metastasis remained elusive. Here, we used liver metastatic human HEP-G2 hepatoma and HT-29LMM colon cancer cells expressing functional CXCR4 to dissect the metastatic cascade by intravital fluorescence microscopy. Immunohistochemistry revealed that the CXCR4 ligand CXCL12 is expressed by endothelial cells and likely Kupffer cells lining the liver sinusoids. Tumor cell adhesion and extravasation in vivo was quantitatively analyzed using intravital fluorescence microscopy. Treatment of cells with an anti-CXCR4 antibody did not affect cell adhesion but significantly impaired tumor cell extravasation (HEP-G2; isotype control: 22.3% ± 4.3% vs anti-CXCR4: 6.0% ± 5.0%, P < .001). In addition, pretreatment of tumor cells with the ligand CXCL12 enhanced the activation of the small GTPases Rho, Rac, and cdc42 as well as tumor cell extravasation without affecting tumor cell adhesion within liver sinusoids. Taken together, the findings of the present study provide first in vivo insights into the early events of chemokine ligand/receptor-mediated liver metastasis formation of tumor cells and define tumor cell extravasation rather than tumor cell arrest as the rate-limiting event.     

Chemokines in neoplastic progression

Chemokines and their receptors have emerged as attractive targets regulating the migration of tumor cells in vivo, a process known as cancer metastasis. The control of metastasis is critical to the control of cancer progression. Two chemokine receptors and their ligands stand out as likely targets for therapeutics: CCR7/CCL21 for lymph node metastases, and CXCR4/CXCL12 for lung, liver, bone marrow, and brain metastases. The most widely expressed chemokine receptor among cancers is likely to be CXCR4.     

The Role of chemokine receptor CXCR4 in breast cancer metastasis

Breast cancer is one of the leading causes of cancer related deaths worldwide. Breast cancer-related mortality is associated with the development of metastatic potential of primary tumor lesions. The chemokine receptor CXCR4 has been found to be a prognostic marker in various types of cancer, including breast cancer. Recent advances in the field of cancer biology has pointed to the critical role that CXCR4 receptor and its ligand CXCL12 play in the metastasis of various types of cancer, including breast cancer. Breast tumors preferentially metastasize to the lung, bones and lymph nodes, all of which represent organs that secrete high levels of CXCL12. CXCL12 acts as a chemoattractant that drives CXCR4-positive primary tumor cells towards secondary metastatic sites leading to the onset of metastatic lesions. Since its discovery in 2001, the CXCR4 field has progressed at a very fast rate and further studies have pointed to the role of CXCR4 in dissemination of tumor cells from primary sites, transendothelial migration of tumor cells as well as the trafficking and homing of cancer stem cells. This review summarizes the information that has been obtained over the years regarding the role of CXCL12-CXCR4 signaling in breast cancer, discusses its potential application to the development of new therapeutic tools for breast cancer control, and elucidates the potential therapeutic challenges which lie ahead and the future directions that this field can take for the improvement of prognosis in breast cancer patients.     

The biological role of the CXCL12/CXCR4 axis in esophageal squamous cell carcinoma

Esophageal cancer is the eighth most common malignant tumor and the sixth leading cause of cancer-related death worldwide. Esophageal squamous cell carcinoma (ESCC) is the main histological type of esophageal cancer, and accounts for 90% of all cancer cases. Despite the progress made in surgery, chemotherapy, and radiotherapy, the mortality rate from esophageal cancer remains high, and the overall 5-year survival rate is less than 20%, even in developed countries. The C-X-C motif chemokine ligand 12 (CXCL12) is a member of the CXC chemokine subgroup, which is widely expressed in a variety of tissues and cells. CXCL12 participates in the regulation of many physiological and pathological processes by binding to its specific receptor, C-X-C motif chemokine receptor type 4 (CXCR4), where it causes embryonic development, immune response, and angiogenesis. In addition, increasing evidence indicates that the CXCL12/CXCR4 axis plays an important role in the biological processes of tumor cells. Studies have shown that CXCL12 and its receptor, CXCR4, are highly expressed in ESCC. This abnormal expression contributes to tumor proliferation, lymph node and distant metastases, and worsening prognosis. At present, antagonists and imaging agents against CXCL12 or CXCR4 have been developed to interfere with the malignant process and monitor metastasis of tumors. This article summarizes the structure, function, and regulatory mechanism of CXCL12/CXCR4 and its role in the malignancy of ESCC. Current results from preclinical research targeting CXCL12/CXCR4 are also summarized to provide a reference for the clinical diagnosis and treatment of ESCC.     

Epigenetic silencing of CXCL12 increases the metastatic potential of mammary carcinoma cells

Expression of the chemokine receptor CXCR4 has been linked with increased metastasis and decreased clinical prognosis in breast cancer. The current paradigm dictates that CXCR4 fosters carcinoma cell metastasis along a chemotactic gradient to organs expressing the ligand CXCL12. The present study asked if alterations in autocrine CXCR4 signaling via dysregulation of CXCL12 in mammary carcinoma cells modulated their metastatic potential. While CXCR4 was consistently detected, expression of CXCL12 characteristic of human mammary epithelium was silenced by promoter hypermethylation in breast cancer cell lines and primary mammary tumors. Stable re-expression of functional CXCL12 in ligand null cells increased orthotopic primary tumor growth in the mammary fat-pad model of tumorigenesis. Those data parallel increased carcinoma cell proliferation measured in vitro with little-to-no-impact on apoptosis. Moreover, re-expression of autocrine CXCL12 markedly reduced metastatic lung invasion assessed using in vivo bioluminescence imaging following tail vein injection. Consistent with those data, decreased metastasis reflected diminished intracellular calcium signaling and chemotactic migration in response to exogenous CXCL12 independent of changes in CXCR4 expression. Together these data suggest that an elevated migratory signaling response to ectopic CXCL12 contributes to the metastatic potential of CXCR4-expressing mammary carcinoma cells, subsequent to epigenetic silencing of autocrine CXCL12.     

Expression of CXCL12 and CXCR4 in pT3-stage gastric cancer does not correlate with peritoneal metastasis

CXCR4, a chemokine receptor, is considered to be involved in the metastastic formation of various types of cancer and could influence survival. More recently, CXCR4 was reported to be associated with peritoneal metastasis in gastric cancer, and CXCL12, its ligand, as a prognostic determinant among gastric cancer of various stages. In order to more specifically delineate the relevance of CXCR4 in peritoneal metastasis, 98 patients with pT3-stage gastric cancer who underwent gastrectomy and detection of intra-abdominal free cancer cells in the peritoneal washing samples were evaluated. Immunostaining with anti-CXCL12 and anti-CXCR4 antibodies were performed for the primary tumor specimens, and correlation of the immunoreactivities with various clinicopathologic factors was evaluated. CXCR4 was detected in 61 specimens and CXCL12 in 76 specimens. No significant correlation was observed between presence of free cancer cells in the peritoneal cavity or development of clinical peritoneal carcinomatosis and expression of either the chemokine or the receptor. On the other hand, there was a trend towards correlation of expression of these molecules with recurrences to the distant lymph nodes or to the liver, although the number of events in these categories were insufficient to reach a statistical significance. In gastric cancer, CXCL12/ CXCR4 axis seems to be more strongly associated with lymphatic or hematogenous metastasis than the establishment of peritoneal deposits.     

The significance of cancer cell expression of the chemokine receptor CXCR4

Malignant cells from at least 23 different types of cancer express the chemokine receptor CXCR4 and respond to its ligand CXCL12. This receptor ligand pair appears to be involved in directed migration of cancer cells to sites of metastasis, increased survival of cancer cells in sub optimal conditions and establishment of a tumour promoting cytokine/chemokine network. Preliminary data from animal models suggest that CXCR4 may be an important therapeutic target in a range of cancers. However CXCR4 plays major roles in embryogenesis, homeostasis and inflammation. This raises questions concerning the specificity of CXCR4 antagonists in the treatment of cancer.